A sash window is comprised of one or more moveable panels or sashes, where each sash forms a frame that may hold multiple panes of glass, and both sashes are themselves mounted into a window frame. A “single hung” sash window ordinarily opens by having one sash member, typically the lower sash, sliding vertically relative to the window frame. An arrangement where both sash members can slide vertically is termed a “double hung sash window” or double hung window. For applications in buildings with tall openings, such as for church windows, triple and quadruple-hung windows have been utilized to accommodate the opening.
Each sash member, being comprised of multiple panes of glass housed in a wood frame of the sash, would be quite heavy for most homeowners to open or close with relative ease. Such sash members have traditionally been fitted with a means of counterbalancing the weight of the window panes and frame of the sash member, where such balancing means even permits small children to raise and lower the heavy sash member. Although advances in the materials used for the construction of sash frames, beyond the use of wood, may have lead to reductions in the final weight of the sash members, any reductions have been largely been offset by the use of the double paned glass arrangement, which was developed to increase thermal efficiency.
The means of counterbalancing the sliding sash windows, in its early and perhaps simplest form, was just a cord attached at one end to a counter weight, with the cord crossing a pulley and, at the opposite end, attaching directly to the window. The mass of the weight in that arrangement is necessarily calibrated to counter the weight of the sash member and the friction of the pulley. If the counterweight were sized excessively, the sash member would be difficult to close and would tend to not remain shut. Conversely, if the counterweight were undersized, the sash member would be difficult to open, and would tend to not remain open.
An early patent, U.S. Pat. No. 395,165 to Morgan, shows an arrangement in which the counterweight was replaced by a reel or drum to collect the cord, and a coiled counterbalancing spring within the drum. A common spring for this application was a negator spring, which is a thin flat metal band that is coiled similar to a tape measure. The Morgan approach eliminated the need for the weights, but necessitated housing a drum having a diameter of significantly size, as well as ordinarily permitting some exposure of the drum to provide access for the cord to run down to and attach to the window. These reels or drums are visible, even today, in the windows of many older homes and apartments. Some of these older balance arrangements also make use of a chain in place of the cord.
Counterbalancing of sash windows in the early to middle part of the twentieth century saw the use of helical coil springs in place of the negator spring and reel combination. An early example is shown by U.S. Pat. No. 2,329,463 to Froelich. The Froelich patent incorporates a helical spring within a tubular member which is rotatably mounted, where the tubular member has a spiral thread on its exterior surface that is designed to be engaged by a member secured to the window frame. As the upper sash window is lowered from its rest position, the tubular member is turned and applies more tension to the spring, so that energy stored in the spring can check the window from falling, and may also help in raising the sash member when desired. The arrangement could similarly be rotated to be preloaded upon installation, to counterbalance the weight of the lower sash member and assist in raising it at the appropriate time. Also, U.S. Pat. No. 3,064,306 to Beasley shows another basic spring arrangement, both of which were advantageous over the Morgan approach for, among other things, the reduction in the depth required to house the reel.
An early example of a balance system with helical coil springs and a block and tackle system for countering the weight of the sash member, is shown by U.S. Pat. No. 3,358,403 to Dinsmore. This basic arrangement is part of a class of similar patents, which have progressively become more streamlined and efficient, and have even been adapted to permit use with a pivotable window.
But a serious deficiency of these inventions—because of the limited envelope of the frame, and the size of the “shoe” on such balance assemblies that must necessarily nest within that envelope—is the limitation that the balance assemblies must be fitted into the frame at an early stage of the window assembly sequence by using an intricate installation procedure. This invention eliminates those restrictions by providing a window balance assembly which is transformable to facilitate installation into the frame with ease and at later stages.